Alright, first things first, we need to get the Firebase CLI up and running. Open up your terminal or command prompt and type in npm install -g firebase-tools. This will install the Firebase CLI globally on your system.

Once that's done, log into Firebase using your Google account by typing firebase login. Easy peasy, right?

Next up, let's initialize a new Cloud Functions project. Navigate to the root directory of your Firebase project and run firebase init functions. When prompted, select JavaScript as your language of choice for writing the Cloud Functions. JavaScript is pretty straightforward and gets the job done.

Now, let's get to the fun part—writing your function! Head over to the functions directory in your project and open up the index.js file. Here's a simple example of an HTTP trigger function:

const functions = require('firebase-functions');

exports.processDataStream = functions.https.onRequest((request, response) => {
 // Your data processing functionality goes here
});

We've named this function processDataStream, and it gets triggered whenever an HTTP request is made. Pretty cool, huh?

After you've written your function, it's time to deploy it. Make sure you're in the root directory of your Firebase project and run firebase deploy --only functions. Firebase will handle the rest and give you a URL for your function once it's successfully deployed.

To trigger the deployed function, simply send a request to the URL provided by Firebase after deployment. You can do this from your app or any service that can make HTTP requests.

Firebase functions can handle HTTPS requests, process the data, and send back a response. Here's an example of how you could process a simple JSON data request:

exports.processDataStream = functions.https.onRequest((request, response) => {
  const inputData = request.body; // The data sent from the app
  
  // Process data here
  const outputData = processData(inputData);
  
  // Send response back to the app
  response.send(outputData);
});

In this example, processData is a placeholder for your own logic to handle the inputData. You can customize it to fit your needs.

If you're working with large-scale data streaming, you might want to look into more robust solutions like Google Cloud's Dataflow, Apache Beam, or Apache Kafka. While Firebase Cloud Functions are powerful, they're not really built for high-volume, real-time data streaming. They're better suited for tasks like responding to events within your Firebase project, running background logic, or handling smaller HTTP requests and responses.